Many lung and prostate cancers, of which small cell lung cancer (SCLC) is a prime example, have a neuroendocrine phenotype, and their growth is stimulated by neuropeptides. Antagonists of several peptides (e.g. bradykinin, substance P. bombesin) have been used in experimental treatment of models of SCLC in animals. Among the most potent of the peptides examined thus far, crosslinked dimers of certain bradykinin antagonist peptides have been efficacious both in vitro and in vivo against strains of SCLC and other tumors (Chan et al., Immunopharmacology 33: 201–204, 1996; Stewart et al., Can. J. Physiol. Pharmacol. 75: 719–724, 1997; Stewart et al., U.S. patent application Ser. No. 5,849,863, issued Dec. 15, 1998). Prostate cancers show a similar neuroendocrine phenotype and are susceptible to neuropeptide antagonists.